1. Field of The Invention
The invention concerns a method and device for comparing two variable analogue signals, e.g. varying in time, such as audio or video signals, these signals being either different or identical but shifted in time.
2. Description of Related Art
To compare two variable analogue signals, a correlation function must be determined between these signals and the values of this function used to verify whether or not identity exists between the signals.
The correlation function is determined by numerical computation methods and implies use of sharp cut-off bandpass filters, analogue-to-digital converters, a system for processing information allowing real-time computation of the correlation function; and a complex processing algorithm capable of identifying and compensating for any shift between the two signals. Systems designed to perform this computation are generally fairly expensive.
Other various devices are used that measure the phase shift between two sine-wave analogue signals of the same frequency. However, these devices cannot be used for signals that are not purely sine-wave, such as audio or video signals received or produced by radio and television receivers.